/* calculate the PSNR difference between two image files */

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <sys/types.h>
#include <sys/stat.h>

int main(int argc, char *argv[])
{
  /* declaring variables */
  FILE *file1, *file2;

  register long i;
  long file_size;

  char *buf1, *buf2;

  struct stat stat1;
  struct stat stat2;

  double x, error, psnr;

  /* parse the command line */
  if (argc!=3) {
    fprintf(stderr, "Invalid number of inputs!\n");
    fprintf(stderr, "Usage: %s file1 file2\n", argv[0]);
    fprintf(stderr, "file1 and file2 have to be of same size.\n");
    exit(1);
  }
  else {
    /* check the file size */
    if ( (stat(argv[1], &stat1)) ) {
      fprintf(stderr, "Cannot open file %s for reading\n", argv[1]);
      exit(2);
    }
    if ( (stat(argv[2], &stat2)) ) {
      fprintf(stderr, "Cannot open file %s for reading\n", argv[2]);
      exit(2);
    }
    if ( stat1.st_size != stat2.st_size ) {
      fprintf(stderr, "file %s and file %s are not the same size.\n",
	    argv[1], argv[2]);
      exit(2);
    }
  }

  /* allocating memory for the two files, of course we don't really need to do
   * that, but I am lazy... */
  if ( (buf1=(char *)malloc(stat1.st_size*sizeof(char))) == NULL ||
       (buf2=(char *)malloc(stat2.st_size*sizeof(char))) == NULL	) {
    fprintf(stderr, "Cannot allocate memory!\n");
    exit(3);
  }
  
  /* open the two files */
  file1 = fopen(argv[1], "rb");
  file2 = fopen(argv[2], "rb");

  /* read the two files */
  fread(buf1, sizeof(char), stat1.st_size, file1);
  fread(buf2, sizeof(char), stat1.st_size, file2);
  fclose(file1);
  fclose(file2);

  /* calculating distortion */
  error = 0.0;
  for (i=0;i<stat1.st_size;i++) {
    x = (unsigned char)(buf1[i]) - (unsigned char)(buf2[i]);
    error += (x * x / stat1.st_size);
  }
  psnr = 10.0 * log10(255*255/error);

  /* output the distortion */
  if ( !strcmp(argv[0], "mse") )
    printf("%g\n", error);
  else if ( !strcmp(argv[0], "psnr") )
    printf("%g\n", psnr);
  else if ( !strcmp(argv[0], "psnrmse") )
    printf("mse: %g PSNR %g\n", error, psnr);

  /* free up memory and exit */
  free(buf1);
  free(buf2);
  return(0);

}